Process of treating metal articles to alloy constituent metals



May 2, 1939- c. G. FINK E1- Al. 2,155,262

PROCESS OF `TREATING METAL ARTCLES TO ALLOY CONSTITUENT 'NH'IJS4 FiledDec. 27, 1932 WOM/ffyl C brom/m1 P/af/'fy C /e ani/7 y m m m Wo s/7 /nyFurnace Low emleraure M n DMENTORS Patented May 2, 1939 UNITED STATESliROCESS F TREATING METAL ARTICIS T0 ALLOY CONSTITUENT METALS Colin e.Fink ana Pincus Deren, New York, N. Y. Application December 27, 1932,Serial No. 648,870

y 16 Claims. This invention relates to a processA of treating metalarticles, to alloy constituent metals, and

provides improvements therein.

Roberts-Austen (Philosophical ATransactions, Royal Society of London,1897, Series A, 187 .p. 383) reviews the writings and work of scientistsfrom the time of Pliny, 'on the subject of the diffusion of metals, (andalso of matter) and states that previous investigators had reported thatm alloys might be formed by placing carefullycleaned pieces of twoconstituent metals in juxtaposition and heating them to the meltingpoint of the alloy to be formed, which was, in some cases 150 below themelting point of the more 16 fusible of the two metals. Lookingbackward,

this article of Roberts-Austen assumes the rank of a classic, and initmay beperceived an adumi bration of the entire modern achievements baseon the emissivity of matter. .In the experiments 20 reported byRobents-Austen, contrary to the present invention, the heats weremaintained for 'long periods of time, thirty-one days, ten days, thirtydays., twenty-nine days, forty-one days, four days, ten days, six days,as compared with minutes according to the present invention, and

the resulting alloys were non-uniform, the proportion ofthe twoconstituents varying progressively from the line of contact of the twometals.

Despite vthe scientific facts and data given by Roberts-Austen and manypatents and publications which have since issued, we are unaware of anypractical application thereof having been made in overcoming the-diflculties in the production of refractory and resistant alloyarticles which have come into commercial use in the last of thearticle.v The alloying according to the.

present process may be effected in a very short time; minutes ascompared with hours according to Vother processes heretofore yused (suchas chromizing and so-called heat-treatment" processes) and may becarried on in air, or in a reducing or non-oxidizing atmosphere in anordinary manner.

'According to our process, an article asa Wire, rod, sheet, strip,shell, etc., is electroformed, or is formed of a metal which is readilyworked, iron, nickel, copper, molybdenum, etc., or a readily workablealloy, (or an article already. so formed), is coated with anelectrodeposit of the metal to be alloyed therewith, and then heated toa temperature wherethe immediate faces of the metals in contact aremolten or virtually so, which is at about the eutectic of the metals incontact, and above. The heating may be, and preferably is, carried outin two stages. In the first stage, the coated metal may be heated to atemperature at which a superficial -layer of oxide is formed on theouter metal, which oxide layer serves to protect the metal beneath theoxide against the much more rapid oxidation which would take place werethe article heated initially to the higher temperature used in thesecond heating stage. Some diffusion of the coating metal into the metalbeneath 1t may take place. In the second heating stage, the temperatureis raised to about the eutectic melting-point, or above where rapiddiffusion and alloying of the metals occurs. At this high temperatureexcessive consumption of the coating metal by oxidation is defeated bythe rapid diffusion and alloying of said coating metal with theunderlying metal.

Contrary to what might be expected, the formed article does not lose itsform when heated at or above the melting point of the eutectic, theprobable explanation being that at any one instant thecomposition of theeutectic only exists at a line within the body of the article, thecomposition maintaining its solid form 'on each side of said line.Therefore, if the component metals are greater or less than theproportions forming the eutectic, the article will not melt, even thoughit be heated to a temperature at or above the tem perature at which theeutectic melts.

'I'he use of a reducing or non-oxidizing atmosphere, such as generallyunderstood, around the articles during heating, while it does notprevent oxidation at the high temperatures employed in our-process,reduces the consumption of the coatlng metal by oxidation, and its useis hence preferred. I

, While we have spoken of the temperature of the eutectic of the alloyas the ltemperature to which the constituent metals of thestartingarticles is to be heated in'effecting a union thereof to form the alloylayer or band having a definite alloy or eutectic composition,nevertheless in practice temperaturesfwhich vary somewhat from' thetemperatures of Vthe melting points of the eutectics given in scientictreatises and tables are employed. A precise rule for all. cases cannotbe given. There is some empiricism in ascertaining-the operatingtemperature. Certain limitations in the means of makinghigh-temperature.

measurements inclusive of optical pyrometers must be recognized.Measurements obtained by the use of such instruments are not precise, acertain amount of variability bein'g inherent in the instrumentsthemselves, and in the perceptions of different users. l(See Fink PatentNo. 2,082,622 for a like instance). ,Moreoven metals are rarelyobtainable in a pure state, and those used in' industry are known tocontain small amounts of other metals and of so-called nonmetals.Commercial iron and steelcommonly contain carbon, manganese, sulphur,phosphorus, silicon, etc. Nickel (electrolytio as well as that producedin a crucible) contains cobalt, iron and copper. Copper contains somecopper oxide. Electrolytic chromium is usually quite pure; but containssome chromium oxide. 'Ihe noble metals almost invariably contain. otherof the noble metals along with -the principal constituent. Thecomposition of the commercial forms of metals generally is similar.

Moreover, the temperature given in scientific tables for the meltingpoint of a eutectic, varies. For example, in the case of iron andchromium, Adcock, Journal Iron and Steel Institute, London, Sept. 1931,gives the temperature of the meltingpoint of the eutectic as 1507 C. VonVegesack, Zeitschrift fr Anorganische Chemie, 154, 30 (1926) gives arange of temperatures for the melting-point of the iron-chromiumeutectic from 1150 C. when the iron used contains 4% carbon to 1490 C.when the iron used containspractically no carbon. These appear to be themost recent data available.

In practice we use a temperature at or about the melting point of theeutectic, at which a rapid alloying of the constituent metals occurs,whilel the article maintains its form, with the forma.- tion of an alloylayer or band having a denite alloy composition, which temperature isusually within about C.l of the temperature of the melting-point of theeutecticv given in scientific tables, for eutecticsv having highmelting-points, for example those above 1000 C.

An example' of our process-is as follows:

An iron wire, or strip, etc., is coated with an electro-deposit ofchromium to any desired thickness. 'Strips and the like may be coated onone `or both sides; The coated wire is then heated in the ordinaryatmosphere of an electrically heatedv ofhydrogen (or in the ordinaryatmosphere of a furnace) at a suitable temperature to form a supercialchromium-'oxide lm on the surface of' the chromium coating; forinstance, at 1000 to 1200u C.-for one to two minutes. The coated articleis then transferred to a furnace and heated in an atmosphere of hydrogen(or in the ordinary atmosphere of an electrically-heatediurnace) at atemperature of 100 to 1500" C. for 3 to 30 minutes, depending on thethickness of the chromium coating. Ordinary commercial hydrogen may beused.

`Another example is as follows: l

A strip of cobalt is electroformed, and then coated with anelectrodeposit of chromium, so that the proportions will be as desired.Alternate layers may be formed. This is then heated to a temperature ator somewhat above lts eutectic melting-point, which was between 1400 to1500 C. A preliminary heating at a lower temperature may' be practiced,if desired.

Other examples of our process are as. follows:

A nickel wire or strip is coated with an electro-deposit of chromium vtoany desired thickness, 0r an iron wire or strip is coated with anelectro-deposit of nickel, or of nickel and chromium, to any desiredthickness. These coated wires or strips, etc. are then heated in themanner hereinbefore described. A preliminary heating, as desired orfound most suitable, as heretofore described, may be practiced.

If the outermost metal-layer is relatively susceptible to oxidation, anelectroplate of a metal which is relatively resistant to oxidation(nickel for example) may be applied before heating. This may be a thindeposit.

Further examples, of alloy sheets, rods, wires,

etc., for which the present process may be usedA 'advantageously are:Ni-Fe; Pt-l'r; Cr-Ni;

sheet, strip, rod wire, etc. (iron for example),

enters a. cleaning bath l0 at a;'from which it enters a washing bath H,as indicated at b. i The sheet, etc., is then electroplated, entering achromium-plating bath l2 for example, as indicated at c. The article maythen be given a protective coating (of nickel,- for example), and Aferthis purpose may enter a washing bath- I3 at d, an acid-dip I8 at e, anda nickel-plating bath I5 at f. It may then enter a washing bath it at g.I1' it is desired to form a' preliminary supercial oxid film in thearticle, it may then go into a low temperature furnace iias indicated ath. The

article enters the furnace l 8 'at i where it is heated toa temperatureat or about the eutectic melting point, or above, to form the alloy.'I'he exit from the furnace it is indicated at lc. The article, as

points above 1000 C. and also above the melting point of the eutectic,an forming an alloy of .the

constituent metals by hea -the coated article at a temperature at orabout ti@ melting point of the eutectic of the metals, which producerapid diffusion while the article maintains its form.

2. 'A process of treating metal articles to alloy constituent metals,which comprises. coating a formed metal article with a solid adherentlayer of another metal in intimate metallic contact with the ilrstmetal, the metals having melting points above 1000 C. and also above themelting point of the eutectic, and forming an alloy of the constituentmetals by heating the coated'article at a temperature at or about themelting point of the eutectic of the metals, which will produce rapiddiffusion while the article maintains its form, in a reducing ornon-oxidizing atmosphere.

3. A process oi' treating metal articles to alloy constituent metals,which comprises coating a formed metal article with a solid adherentlayer of another metal in intimate metallic contact with the rst metal,the metals having melting points above 1000 C. and also above themelting point of the eutectic, heating the coated articleto form asupercial oxide iilm thereon, and thereafter forming an alloy of theconstituent metals by heating the coated article at or about the meltingpoint of the eutectic of the metals, which will produce rapid diffusionwhile the article maintains its form.

4. A process of treating metal articles to alloy constituent metals,which comprises coating a formed metal article with a solid adherentlayer of another metal in intimate metallic contact with the rst metal,the metals having melting points above 1000 C. and also above themelting point yof the eutectic, heating the coated article in a reducingor non-oxidizing atmosphere to form a superficial oxide i'llm thereon,and thereafter forming an alloy of the constituent metals by heating thecoated article at or about the melting point of the eutectic of themetals, which will produce rapid diffusion while the' article maintainsits form.

5. A process'of treating metal articles to alloy constituent metals,which comprises coating a formed metal article with a solid adherentlayer oi' another metal in intimate metallic contact with vthe rstmetal, the metals having melting points above 1000 C. and also above themelting point of the eutectic, heating the coated article to form asupercial oxide lm thereon, and thereafter forming an alloy of theconstituent metals by yheating the coated article in a reducing ornon-oxidizing atmosphere at or about the melting point of the eutecticof the metals, which will produce rapid diffusion while the articlemaintains its form.

6. A process of treating metal articles to alloy constituent metals,which comprises coating a formed metal article with a solid adherentlayer of another metal in intimate metallic contact with the ilrstmetal, the metals having melting points above 1000 C. and also above themelting point of the eutectic, heating the coated article to form asuperficial oxide lm thereon, and thereafter forming anI alloy oi.' theconstituent metals by heating the coated article at or about the meltingpoint of the eutectic oi' the metals, which will produce rapiddiilfusion while the article maintains its form, both heatings beingdone in an ordinary reducing or non-oxidizing atmosphere whichincidentally contains some oxygen.

7. A process according to claim 1, further-comprising coating theoutermost coat with a coat of a metal less susceptible to oxidation athigh tem- 8. A process according to claim 1 wherein the article which iscoated is electroformed.

9. In a process of treating metal articles to alloy constituent metals,forming an alloy of the constituent metals by heating a metal articlehaving thereon a solid adherent coating metal in intimate metalliccontact with the ilrst metal, the metals having melting points above1000 C. and also above the melting point of the eutectic, at atemperature at or about the melting point of the eutectic of the metals,which will produce lrapid diffusion while the article maintains itsform.

10. In a process of treating metal articles to alloy constituent metalsforming an alloy of the constituent metals by heating a metal articlehaving thereon a solid adherent coating metal in intimate metalliccontact with the rstmetal to form a superiicial oxide lm thereon, saidmetals having melting points above 1000 C. and also above the meltingpoint of the eutectic, and thereafter heating at a temperature at orabout the melting-point of the eutectic of the metals, which willproduce rapid diffusion while the article maintains its form.

11. In a process of treating metal articles to alloy constituent metals,coating the outermost coat of a coated metal article with a coat ofmetal less susceptible to oxidation at high temperature than saidoutermost coat, said metal and coating having melting points above 1000C. and also above the meltingpoint of the eutectic, and then forming analloy of the constituent metals by heating at a temperature at or aboutvthe melting-point of the eutectic of the metals, which will producerapid diffusion while the metal maintains its form.

12. In a process of forming ferro-chromium alloy articles, alloying theconstituents by heatin g an article comprising layers of iron and vchromium in intimatemetallic contact at a temperature at or about thetemperature of the melting point of the eutectic, between 1400 to 1500"C. for a relatively short time while the metals rapidly diiuse and thearticle maintains its form.

13. In a process of forming ferro-chromium alloy articles, according toclaim 12, preliminarily heating said article at a lower temperature todevelop a thin protective oxid lm thereon.

14. In a process of forming ferro-nickel-chromium alloy articles,alloying the constituents by heating an article comprising layers ofiron, nickel and chromium in intimate metallic contact at a. temperatureat or about the temperature of the melting point of the eutectic, above1400 C. for a relatively short time while the metals rapidly diffuse andthe article maintains its form.

15. In a process of forming ferro-nickel-chromium alloyarticlesaccording to claim 14, preliminarily heating said article at a lowertemperature to develop a thin protective oxid nlm there- 16. In aprocess of forming alloy articles, alloying the constituents by heatingan article comprising layers of metals in -intimate metallic contacthaving melting points above 1400 C. at a temperature at or aboutthemelting point of the eutectic of the metals for a relative short timewhile the metals rapidly diffuse and the article -maintains its form.

